UP TO a third of drug users could also be taking other people's ADHD medications, according to a study that shows strict crackdowns on stimulant medication prescriptions are failing to stop illicit trade in the drugs. The study of people who were regularly using other illicit stimulant drugs such as methamphetamine found 31 per cent of them had used medications that had been prescribed to other people to treat conditions such as ADHD or narcolepsy.